I. Field of the Invention
The present invention relates generally to a method and apparatus for monitoring the quality of a machining operation, such as a friction stir welding operation.
II. Description of Related Art
There are many different types of machining operations which utilize an electric motor to control the movement of the tool. For example, such machining operations include friction stir welding, milling, drilling, etc.
The proper control of the movement of the machining tool during a machining operation is oftentimes indicative of the quality of the final machined part. For example, during a friction stir welding operation, an insufficient plunge of the pin into the part during the friction stir welding operation will oftentimes result in an inadequate and unacceptable weld.
There have been a number of previously known control strategies employed in the industrial manufacturing industry which monitor various parameters during the machining operation as a form of quality control for that machining operation. For example, some previously known systems have utilized transducers to monitor the condition of the part during the machining operation.
These previously known systems which have utilized such sensors, however, have not proven wholly satisfactory in use. Such sensors can significantly add to the overall cost of the system and may require complex and time-consuming calibration. Furthermore, the performance of such sensors often deteriorates over time and thus results in false readings from the sensors.
A still further disadvantage of these previously known sensors employed to monitor the quality of the machining operation is that the control systems have only monitored the instantaneous values of the sensor outputs in order to ensure that the sensor output falls within a preset range. These sensors, however, are oftentimes subject to industrial environments which contain a great detail of electrical noise. Such noise can influence the output from the sensors and thus result in false readings. Such false readings can indicate that a machined part meets the required quality standards when, in fact, it does not, and vice versa.